Phase locked loop (pll) with multi-phase time-to-digital converter (tdc)

ABSTRACT

One or more techniques or systems for locking a phase locked loop (PLL) are provided herein. In some embodiments, a multi-phase time-to-digital converter (TDC) includes a first phase finder, a phase predictor, a second phase finder, and a phase switch. For example, the first phase finder is configured to generate a first fractional phase signal based on a multi-phase variable clock (CKV) signal. For example, the phase predictor is configured to generate a phase select (QSEL) signal or a multi-phase CKV select (CKVSEL) signal based on a frequency command word (FCW) signal or the multi-phase CKV signal. For example, the second phase finder is configured to generate a second fractional phase signal based on the CKVSEL signal or the QSEL signal. For example, the phase switch is configured to select the first or second fractional phase signal based on a phase error (PHE) signal.

RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 13/755,159, filed on Jan. 31, 2013 and entitled“PHASE LOCKED LOOP (PLL) WITH MULTI-PHASE TIME-TO-DIGITAL CONVERTER(TDC),” which is incorporated herein.

BACKGROUND

Generally, a phase locked loop (PLL) generates an output signalassociated with a phase related to a phase of an input signal. Some PLLsuse a counter to report an integer phase of a digitally controlledoscillator (DCO). Additionally, some PLLs use a time-to-digitalconverter (TDC) to report a fractional phase of the DCO. However,managing power consumption and area associated with a PLL or a TDCbecomes challenging with more advanced technology.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to be an extensive overview ofthe claimed subject matter, identify key factors or essential featuresof the claimed subject matter, nor is it intended to be used to limitthe scope of the claimed subject matter.

One or more techniques or systems for locking a phase locked loop (PLL)are provided herein. In some embodiments, a PLL comprises a multi-phasetime-to-digital converter (TDC). In some embodiments, the multi-phaseTDC is configured to generate a first fractional phase signal of amulti-phase variable clock (CKV) signal based on at least one of themulti-phase CKV signal or a reference frequency (FREF) signal. In someembodiments, the multi-phase CKV signal is associated with one or moreclock signals and one or more corresponding phases. As an example, someCKV signals are four-phase CKV signals. In this example, a four-phaseCKV signal comprises a first signal associated with a first phase, asecond signal associated with a second phase, a third signal associatedwith a third phase, and a fourth signal associated with a fourth phase.In some embodiments, the multi-phase TDC is configured to generate asecond fractional phase signal of the multi-phase CKV signal based on atleast one of the multi-phase CKV signal, a frequency command word (FCW)signal, or a phase reference (PHR) signal. In some embodiments, thephase switch is configured to select at least one of the firstfractional phase signal or the second fractional phase signal based on aphase error (PHE) signal. In this way, the PLL comprising themulti-phase TDC is configured for reduced power consumption, at leastbecause the first phase finder is off when the second phase finder andthe phase predictor are on. Additionally, the second phase finder andthe phase predictor are off when the first phase finder is on.Accordingly, power consumption is reduced for the PLL or multi-phaseTDC, at least because the first phase finder toggles on or off based onthe second phase finder and the phase predictor. It will be appreciatedthat a number of inverters associated with the multi-phase TDC isreduced, at least because the second phase finder is configured to covera portion of a clock generated by a digitally controlled oscillator(DCO), such as a portion of the CKV. Accordingly, it will be appreciatedthat power consumption or area associated with the multi-phase TDC ismitigated in this way, at least because the number of invertersassociated with the multi-phase TDC is reduced.

The following description and annexed drawings set forth certainillustrative aspects and implementations. These are indicative of but afew of the various ways in which one or more aspects are employed. Otheraspects, advantages, or novel features of the disclosure will becomeapparent from the following detailed description when considered inconjunction with the annexed drawings.

DESCRIPTION OF THE DRAWINGS

Aspects of the disclosure are understood from the following detaileddescription when read with the accompanying drawings. It will beappreciated that elements, structures, etc. of the drawings are notnecessarily drawn to scale. Accordingly, the dimensions of the same maybe arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic diagram of an example multi-phase time-to-digitalconverter (TDC), according to some embodiments.

FIG. 2 is a schematic diagram of an example phase locked loop (PLL)associated with a multi-phase time-to-digital converter (TDC), accordingto some embodiments.

FIG. 3 is a schematic diagram of an example first phase finder,according to some embodiments.

FIG. 4 is a schematic diagram of an example phase predictor, accordingto some embodiments.

FIG. 5 is a schematic diagram of an example second phase finder,according to some embodiments.

FIG. 6 is a schematic diagram of an example phase switch, according tosome embodiments.

FIG. 7 is a flow diagram of an example method for locking a phase lockedloop (PLL), according to some embodiments.

FIG. 8 is a flow diagram of an example method for locking a phase lockedloop (PLL), according to some embodiments.

FIG. 9 is a flow diagram of an example method for designing a phaselocked loop (PLL), according to some embodiments.

DETAILED DESCRIPTION

Embodiments or examples, illustrated in the drawings are disclosed belowusing specific language. It will nevertheless be understood that theembodiments or examples are not intended to be limiting. Any alterationsand modifications in the disclosed embodiments, and any furtherapplications of the principles disclosed in this document arecontemplated as would normally occur to one of ordinary skill in thepertinent art.

FIG. 1 is a schematic diagram of an example multi-phase time-to-digitalconverter (TDC) 100, according to some embodiments. In some embodiments,the multi-phase TDC 100 comprises a first phase finder 110, a phasepredictor 130, a second phase finder 120, and a phase switch 140. Insome embodiments, the first phase finder 110 comprises a first input, asecond input, and an output. For example, the first input of the firstphase finder 110 is connected to a reference frequency (FREF) line 102associated with a FREF signal. For example, the second input of thefirst phase finder 110 is connected to a multi-phase variable clock(CKV) line 104 associated with a multi-phase CKV signal. In someembodiments, the first phase finder 110 is configured to generate afirst fractional phase signal at the output of the first phase finder110. In some embodiments, the output of the first phase finder 110 isconnected to a first fractional phase line 112. In some embodiments, theoutput of the first phase finder 110 is connected to a first input ofthe phase switch 140 via the first fractional phase line 112.

It will be appreciated that the multi-phase TDC 100 is configuredaccording to a multi-phase CKV. In some embodiments, the multi-phase CKVis a four-phase CKV. However, it will be appreciated that at least oneof the multi-phase TDC 100 or the multi-phase CKV is associated with anumber of phases other than four in some embodiments.

In some embodiments, the first phase finder 110 is configured togenerate the first fractional phase signal of the multi-phase CKV signalbased on at least one of the multi-phase CKV signal or the FREF signal.It will be appreciated that the multi-phase CKV signal is associatedwith one or more clock signals and one or more corresponding phases. Insome embodiments, the first phase finder 110 is configured to generate afirst fractional phase signal of a four-phase variable clock (CKV)signal based on at least one of the four-phase CKV signal or a referencefrequency (FREF) signal. For example, a four-phase CKV signal comprisesa first clock signal associated with a first corresponding phase, asecond clock signal associated with a second corresponding phase, athird clock signal associated with a third corresponding phase, and afourth clock signal associated with a fourth corresponding phase. Insome embodiments, the first clock signal, the second clock signal, thethird clock signal, and the fourth clock signal are associated withsubstantially similar frequencies. In some embodiments, respectivephases are defined by increments of three hundred and sixty degreesdivided by a number of phases. For example, for the four-phase CKVsignal, the first phase is associated with at least about zero degrees,the second phase is associated with at least about ninety degrees, thethird phase is associated with at least about one hundred and eightydegrees, and the fourth phase is associated with at least about twohundred and seventy degrees. In this way, the first phase finder 110 isconfigured to select a clock signal and corresponding phase from atleast one of the one or more clock signals. For example, the first phasefinder 110 is configured to select the clock signal associated with aphase closest to a phase of the FREF signal. As an example, if the FREFsignal is associated with a phase of ten degrees and the CKV is afour-phase CKV, the first phase finder 110 is configured to select thefirst clock signal associated with the first phase of at least aboutzero degrees. In this way, the first phase finder 110 is configured togenerate the first fractional phase signal in a quick fashion, at leastbecause the first fractional phase signal is generated based on a numberof phases associated with the multi-phase CKV signal.

In some embodiments, the phase predictor 130 comprises a first input, asecond input, a third input, a first output, and a second output. Forexample, the first input of the phase predictor 130 is connected to themulti-phase variable clock (CKV) line 104 associated with themulti-phase CKV signal. For example, the second input of the phasepredictor 130 is connected to a phase reference (PHR) line 106associated with a PHR signal. In some embodiments, the PHR signal is areference phase associated with the FREF signal. For example, the thirdinput of the phase predictor 130 is connected to a frequency commandword (FCW) line 108 associated with a FCW signal. In some embodiments,the phase predictor 130 is configured to generate a phase select (QSEL)signal at the first output of the phase predictor 130. In someembodiments, the first output of the phase predictor 130 is connected toa QSEL line 132. In some embodiments, the first output of the phasepredictor 130 is connected to a first input of the second phase finder120 via the QSEL line 132. In some embodiments, the phase predictor 130is configured to generate a multi-phase CKV select (CKVSEL) signal atthe second output of the phase predictor 130. In some embodiments, thesecond output of the phase predictor 130 is connected to a CKVSEL line134. In some embodiments, the second output of the phase predictor 130is connected to a second input of the second phase finder 120 via theCKVSEL line 134.

In some embodiments, the phase predictor 130 is configured to generateat least one of the CKVSEL signal or the QSEL signal based on at leastone of the multi-phase CKV signal, the PHR signal, or the FCW signal. Insome embodiments, the QSEL signal is generated based on at least one ofthe PHR signal or the FCW signal. In some embodiments, the CKVSEL signalis generated based on at least one of the QSEL signal or the multi-phaseCKV signal. In some embodiments, the QSEL signal is associated with amapping of a fractional portion of the FCW signal. It will beappreciated that the multi-phase CKV signal is associated with one ormore clock signals and one or more corresponding phases. In someembodiments, the CKVSEL signal is generated based on a selection of atleast one of the one or more clock signals and corresponding phases. Inthis way, the phase predictor 130 is configured to provide the secondphase finder 120 with at least one of a clock signal or an associatedoffset, thereby facilitating phase locking for the second phase finder120. In other words, the CKVSEL signal is configured to mitigateprocessing time or power consumption associated with the second phasefinder 120, at least because the CKVSEL signal is a clock signalassociated with a phase offset. Additionally, it will be appreciatedthat the QSEL signal is indicative of the phase offset according to someembodiments. In this way, at least one of the CKVSEL signal or the QSELsignal generated by the phase predictor 130 enables quicker processingor reduced power consumption. For example, if a PHR signal is associatedwith a fractional part from at least about 0.75 to at least about 1.00,the phase predictor 130 is configured to select a fourth clock signalassociated with a two hundred and seventy degree phase from the one ormore multi-phase CKV signals to be the CKVSEL signal. Additionally, theFCW signal is used to generate the QSEL signal and predict a next CKVfractional phase.

In some embodiments, the second phase finder 120 comprises a firstinput, a second input, a third input, and an output. For example, thefirst input of the second phase finder 120 is connected to the QSEL line132 associated with the QSEL signal. For example, the second input ofthe second phase finder 120 is connected to the CKVSEL line 134associated with the CKVSEL signal. For example, the third input of thesecond phase finder 120 is connected to the FREF line 102 associatedwith the FREF signal. In some embodiments, the second phase finder 120is configured to generate a second fractional phase signal at the outputof the second phase finder 120. In some embodiments, the output of thesecond phase finder 120 is connected to a second fractional phase line122. In some embodiments, the output of the second phase finder 120 isconnected to a second input of the phase switch 140 via the secondfractional phase line 122.

In some embodiments, the second phase finder 120 is configured togenerate the second fractional phase signal based on at least one of theFREF signal, the CKVSEL signal, or the QSEL signal. For example, thesecond phase finder 120 is configured to determine a phase distancebetween the CKVSEL signal and the FREF signal. In some embodiments, thephase distance is a phase difference expressed in units of time. In someembodiments, the second phase finder 120 is configured for multi-phaseCKV operation, at least because the second phase finder 120 comprises anumber of inverters associated with a digitally controlled oscillator(DCO) clock period divided by a number of phases associated with the CKVclock period of the DCO. For example, if a CKV clock period is eightynanoseconds long, the CKV is a four-phase CKV, and an inverter isassociated with a ten nanosecond delay, the second phase finder 120comprises at least about two inverters, at least because two inverterscovers at least about twenty nanoseconds. In other words, the secondphase finder 120 is configured to cover a quarter of the CKV clockperiod when the CKV is a four-phase CKV. Explained another way, thesecond phase finder 120 is configured to cover at least about one fourthof a DCO period based on a four-phase CKV signal. In this way, area andpower consumption associated with additional inverters is mitigated, atleast because six inverters are not required to cover the other threequarters of the CKV clock period. Accordingly, the second phase finder120 is thus not required to cover the CKV clock period. In someembodiments, the second phase finder 120 comprises a number of invertersassociated with the clock period divided by the number of phasesassociated with the CKV. In this way, the number of inverters associatedwith the second phase finder 120 is mitigated, thereby mitigating powerconsumption.

In some embodiments, a unit of time associated with the phase differenceis based on an inverter delay. For example, if the CKVSEL signal istwenty nanoseconds from the FREF signal, and an inverter is associatedwith a ten nanosecond delay, the second phase finder 120 is configuredto determine that there is a two inverter difference between the CKVSELsignal and the FREF signal. In some embodiments, the second phase finder120 is configured to convert the phase difference expressed in units oftime into a phase difference expressed in degrees. Additionally, thesecond phase finder 120 is configured to convert the QSEL signal into anoffset expressed in degrees. Accordingly, the second phase finder 120 isconfigured to generate a second fractional phase signal indicative of aphase difference between a first clock of the multi-phase CKV signal andthe FREF signal. In this way, no high speed multiplexing or timeamplifiers are required, at least because the multi-phase TDC 100 isconfigured to switch between the first phase finder 110 and the secondphase finder 120.

In some embodiments, the phase switch 140 comprises a first input, asecond input, a third input, and an output. For example, the first inputof the phase switch 140 is connected to the first fractional phase line112 associated with the first fractional phase signal. For example, thesecond input of the phase switch 140 is connected to the secondfractional phase line 122 associated with the second fractional phasesignal. For example, the third input of the phase switch 140 isconnected to a phase error (PHE) line 138 associated with a PHE signal.In some embodiments, the phase switch 140 is configured to generate afractional variable phase correction (PHVF) signal at the output of thephase switch 140. In some embodiments, the output of the phase switch140 is connected to a PHVF line 142. In some embodiments, the phaseswitch 140 is configured to select the first fractional phase signalwhen the PHE is at least one of greater than or equal to at least aboutninety degrees. In some embodiments, the phase switch 140 is configuredto select the second fractional phase signal when the PHE is less thanat least about ninety degrees. In some embodiments, the first phasefinder 110 is turned off when at least one of the second phase finder120 or the phase predictor 130 is on. In some embodiments, at least oneof the second phase finder 120 or the phase predictor 130 is turned offwhen the first phase finder 110 is on. In this way, power consumptionassociated with at the multi-phase TDC 100 is mitigated. In someembodiments, the phase switch 140 is configured to disable the secondphase finder 120 when the first phase finder 110 is enabled. In someembodiments, the phase switch 140 is configured to enable the secondphase finder 120 when the first phase finder 110 is disabled.

FIG. 2 is a schematic diagram of an example phase locked loop (PLL) 200associated with a multi-phase time-to-digital converter (TDC), accordingto some embodiments. In some embodiments, the PLL 200 of FIG. 2 is anall digital phase locked loop (ADPLL). In some embodiments, the PLL 200comprises a accumulator component 210, an adder component 220, a loopfilter 230, a digitally controlled oscillator (DCO) 240, a sigma deltamodulation component 260, a frequency divider 250, a counter component270, and a multi-phase time-to-digital converter (TDC) 100.

In some embodiments, the accumulator component 210 comprises an inputand an output. For example, the input of the accumulator component 210is connected to a frequency command word (FCW) line 108 associated witha FCW signal. Additionally, the accumulator component 210 comprises asecond input connected to the FREF line 102. For example, the output ofthe accumulator component 210 is connected to a phase reference (PHR)line 106 associated with a PHR signal. In some embodiments, theaccumulator component 210 is connected to an input of at least one ofthe adder component 220 or the multi-phase TDC 100. In some embodiments,the accumulator component 210 is configured to generate the PHR signalbased on at least one of the FCW signal or the FREF signal.

In some embodiments, the adder component 220 comprises an input, asecond input, a third input, and an output. For example, the input ofthe adder component 220 is connected to the PHR line 106 associated withthe PHR signal. For example, the second input of the adder component 220is connected to a fractional variable phase correction (PHVF) line 142associated with a PHVF signal. For example, the third input of the addercomponent 220 is connected to an integer variable phase correction(PHVI) line 272 associated with a PHVI signal. For example, the outputof the adder component 220 is connected to a phase error (PHE) line 138associated with a PHE signal. In some embodiments, the adder component220 is connected to an input of at least one of the loop filter 230 orthe multi-phase TDC 100.

In some embodiments, the adder component 220 is configured to generatethe PHE signal based on at least one of the PHR signal, the PHVI signal,or the PHVF signal. In some embodiments, the adder component 220 isconfigured to determine a phase difference between the PHR signal andthe multi-phase CKV signal generated by the DCO 240, at least because atleast one of the multi-phase TDC 100 or the counter component 270generates at least one of the PHVF or PHVI signal based on themulti-phase CKV signal. In this way, the adder component facilitates alock for the PLL 200.

In some embodiments, the loop filter 230 comprises an input and anoutput. For example, the input of the loop filter 230 is connected tothe PHE line 138 associated with the PHE signal. For example, the outputof the loop filter 230 is connected to an input of at least one of theDCO 240 or the sigma delta modulation component 260 via 232. In someembodiments, the loop filter 230 is configured to filter at least someof the PHE signal and generate an output at 232.

In some embodiments, the DCO 240 comprises an input, a second input, andan output. For example, the input of the DCO 240 is connected to theloop filter 230 via 232. For example, the second input of the DCO 240 isconnected to the sigma delta modulation component 260 via 262. Forexample, the output of the DCO 240 is connected to a multi-phasevariable clock (CKV) line 104 associated with a multi-phase CKV signal.In some embodiments, the DCO 240 is connected to an input of at leastone of the multi-phase TDC 100, a first phase finder 110, a phasepredictor 130, the counter component 270, or the frequency divider 250.In some embodiments, the DCO 240 is configured to generate themulti-phase CKV signal based on at least one of an output from the loopfilter 230 or an output from the sigma delta modulation component 260.In some embodiments, the DCO 240 is configured to generate themulti-phase CKV signal associated with one or more clock signals and oneor more corresponding phases. For example, for a four-phase CKV, the DCO240 is configured to generate a first clock signal associated with azero degree phase, a second clock signal associated with at least abouta ninety degree phase, a third clock signal associated with at leastabout a one hundred and eighty degree phase, and a fourth clock signalassociated with at least about a two hundred and seventy degree phase.It will be appreciated that at least one of the first clock signal, thesecond clock signal, the third clock signal, or the fourth clock signalis associated with a same frequency as at least one of the other clocksignals in some embodiments. Additionally, a degree increment associatedwith a phase of a clock signal is equal to at least about three hundredand sixty divided by a number of phases associated with the multi-phaseCKV signal.

In some embodiments, the frequency divider 250 comprises an input and anoutput. For example, the input of the frequency divider 250 is connectedto the CKV line 104 associated with the multi-phase CKV signal. Forexample, the output of the frequency divider 250 is connected to asecond input of the sigma delta modulation component 260. In someembodiments, the frequency divider 250 is configured to divide themulti-phase CKV signal by fixed number. For example, the fixed number isselected to be a number of phases associated with the multi-phase CKVsignal. If the multi-phase CKV signal is a four-phase CKV signal, thefrequency divider 250 is configured to divide the multi-phase CKV signalby four. That is, if the input of the frequency divider 250 is eightgigahertz, the output of the frequency divider is two gigahertz.

In some embodiments, the sigma delta modulation component 260 comprisesan input, a second input, and an output. For example, the input of thesigma delta modulation component 260 is connected to the loop filter 230via 232. For example, the second input of the sigma delta modulationcomponent 260 is connected to the frequency divider 250 via 252. Forexample, the output of the sigma delta modulation component 260 isconnected to a second input of the DCO 240 via 262.

In some embodiments, the counter component 270 comprises an input and anoutput. For example, the input of the counter component 270 is connectedto the CKV line 104 associated with the multi-phase CKV signal. Forexample, the output of the counter component 270 is connected to atleast one of an integer variable phase correction (PHVI) line 272associated with a PHVI signal or a third input of the adder component220. In some embodiments, the counter 270 is configured to at least oneof generate or report an integer phase of the DCO 240, such as the PHVIsignal, based on the CKV generated by the DCO 240. In some embodiments,the counter component 270 is configured to lock the DCO 240 to a samefrequency as the FREF signal based on the multi-phase CKV signal.

In some embodiments, the multi-phase TDC 100 comprises one or moreinputs and an output. For example, an input of the one or more inputs ofthe multi-phase TDC 100 is connected to at least one of the FCW line 108associated with the FCW signal, the PHR line 106 associated with the PHRsignal, the PHE line 138 associated with the PHE signal, the FREF line102 associated with the FREF signal, or the multi-phase CKV line 104associated with the multi-phase CKV signal. For example, the output ofthe multi-phase TDC 100 is connected to the PHVF line 142 associatedwith the PHVF signal. In some embodiments, the multi-phase TDC 100 isconnected to a second input of the adder component 220. In someembodiments, the multi-phase TDC 100 is configured to at least one ofgenerate or report a fractional phase of the DCO 240, such as the PHVFsignal, based on the CKV generated by the DCO 240. In some embodiments,the multi-phase TDC 100 is configured to lock the CKV generated by theDCO 240 to a same phase as at least one of the FREF signal or the PHRsignal based on the multi-phase CKV signal. In some embodiments, anoutput of a phase switch 140 is connected to an input of the addercomponent 220 via a PHVF line 142 associated with a PHVF signal.

FIG. 3 is a schematic diagram of an example first phase finder 110,according to some embodiments. In some embodiments, the first phasefinder 110 comprises a first flip flop (FF) 302, a second FF 304, athird FF 306, a fourth FF 308, an AND gate 310, an OR gate 320, and aninverter 330. In some embodiments, the first phase finder 110 isconfigured to generate a binary code associated with at least one of afirst clock, a second clock, a third clock, or a fourth clock. In someembodiments, the first phase finder 110 of FIG. 3 is configured togenerate a first fractional phase signal for a four-phase CKV. In someembodiments, the first phase finder 110 of FIG. 3 is configured tooperate when the PHE is greater than or equal to at least about ninetydegrees. In some embodiments, the first FF 302 is connected to a FREFline 102 and a multi-phase CKV line 104. Similarly, at least one of thesecond FF 304, the third FF 306, or the fourth FF 308 is connected tothe FREF line 102 and the multi-phase CKV line 104. In some embodiments,the AND gate 310 comprises a first input, a second inverted input, andan output. For example, the first input of the AND gate 310 is connectedto an output of the third FF 316. In some embodiments, the secondinverted input of the AND gate 310 is connected to an output of thesecond FF 314. In some embodiments, the OR gate 320 comprises a firstinverted input, a second input, and an output. For example, the firstinverted input of the OR gate 320 is connected to an output of thefourth FF 318. For example, the second input of the OR gate 320 isconnected to the output of the AND gate 312. In some embodiments, theinverter 330 comprises an input and an output. For example, the input ofthe inverter 330 is connected to the output of the third FF 316. Forexample, the output of the inverter 330 is associated with a second bitfor the first fractional phase signal. For example, the output of the ORgate 320 is associated with a first bit for the first fractional phasesignal. In some embodiments, the first fractional phase signal comprisesthe first bit and the second bit. In some embodiments, the output of theinverter 330 is connected to a second bit line 112B and the output ofthe OR gate 320 connected to a first bit line 112A.

FIG. 4 is a schematic diagram of an example phase predictor 130,according to some embodiments. In some embodiments, the phase predictor130 comprises a phase forward component 410 and a multiplexer (MUX) 420.In some embodiments, the phase forward component 410 is configured togenerate a QSEL signal based on at least one of a FCW signal or a PHRsignal. In some embodiments, the phase forward component 410 isconnected to at least one of an FCW line 108 associated with the FCWsignal or a PHR line 106 associated with the PHR signal. In someembodiments, the MUX 420 is configured to generate a CKVSEL signal byselecting at least one of one or more clock signals associated with CKVand corresponding phases based on the QSEL signal. In some embodiments,an output of the phase forward component is connected to at least one ofa QSEL line 133 or the MUX 420. In some embodiments, the phase predictor130 of FIG. 4 is configured to generate the CKVSEL signal based on afour-phase CKV. In some embodiments, the MUX 420 is connected to one ormore multi-phase CKV lines 104A, 104B, 104C, or 104D. In someembodiments, the multi-phase CKV line is associated with at least one ofthe one or more CKV lines 104A, 104B, 104C, or 104D. In someembodiments, an output of the MUX 420 is connected to a CKVSEL line 134.In this way, the MUX 420 is configured to generate the CKVSEL signal.

FIG. 5 is a schematic diagram of an example second phase finder 120,according to some embodiments. In some embodiments, the second phasefinder 120 comprises one or more delay units, a thermometer decoder 510,a time phase converter 520, a shift register 530, and an adder component540. In some embodiments, a delay unit 590 of the one or more delayunits comprises a first inverter 504 and a first flip flop (FF) 514. Insome embodiments, an inverter comprises an input and an output. Forexample, the input of the inverter is connected to at least one of aCKVSEL line 134 or an output of a second inverter 502A of a second timedelay unit. In some embodiments, a FF comprises an output. For example,a FF is connected to at least one of the CKVSEL line 134, the output ofthe second inverter 502A, or a FREF line 102. In some embodiments, thesecond phase finder 120 comprises N number of delay units, where the Nthdelay unit comprises an Nth inverter 50N and an Nth FF 51N. In someembodiments, the thermometer decoder 510 is connected to one or moreoutput of respective FFs. For example, the thermometer decoder 510 isconnected to an output of the first FF 512A, an output of the second FF514A, etc. In some embodiments, the time phase converter 520 isconnected to the thermometer decoder 510. In some embodiments, the shiftregister 530 is connected to a QSEL line 132. In some embodiments, theadder component 540 is connected to the timer phase converter 520 andthe shift register 530. In some embodiments, the thermometer decoder 510is configured to determine a time difference between the FREF signal andthe CKVSEL signal. Generally, an inverter is associated with a delaytime such that an output is produced for the inverter the delay timeafter the input is provided. The time difference between the FREF signaland the CKVSEL signal is expressed as a number of units, such as anumber of inverters strung together in series in order for the string ofinverters to approximate the time difference between the FREF signal andthe CKVSEL signal. In some embodiments, the time phase converter 520 isconfigured to determine a degree phase difference between the FREFsignal and the CKVSEL signal based on an output of the thermometerdecoder 510A. In some embodiments, the adder component 540 is configuredto determine a degree phase difference between the FREF signal and themulti-phase CKV signal. For example, the output of the shift register530A is associated with an offset between CKVSEL and a first CKV clocksignal. Additionally, the output of the time phase converter 520 isassociated with a phase difference between the CKVSEL signal and theFREF signal. Accordingly, the adder component 540 is configured todetermine a second fractional phase signal based on 530A and 520A.

FIG. 6 is a schematic diagram of an example phase switch 140, accordingto some embodiments. In some embodiments, the phase switch 140 comprisesan adder component 620, a flip flop (FF) 630, a comparator 640, and amultiplexer (MUX) 610. In some embodiments, the adder component 620 isconnected to a PHE line 138 associated with a PHE signal. In someembodiments, the FF 630 is connected to an output of the adder component622. In some embodiments, an output of the FF 632 is connected to theadder component 620. In some embodiments, the comparator 640 isconnected to the output of the FF 632. In some embodiments, the MUX 610is connected to an output of the comparator 642. In some embodiments,the MUX 610 is connected to at least one of a first fractional phaseline 112 or a second fractional phase line 122. In some embodiments, theMUX 610 is configured to select at least one of a first fractional phasesignal or a second fractional phase signal based on the output of thecomparator 642.

FIG. 7 is a flow diagram of an example method 700 for locking a phaselocked loop (PLL), according to some embodiments. In some embodiments,the method 700 comprises generating a first fractional phase signal of amulti-phase variable clock (CKV) signal based on at least one of themulti-phase CKV signal or a reference frequency (FREF) signal at 702.For example, the multi-phase CKV signal associated with one or moreclock signals and one or more corresponding phases. In some embodiments,the method 700 comprises generating a second fractional phase signal ofthe multi-phase CKV signal based on at least one of the multi-phase CKVsignal, a frequency command word (FCW) signal, or a phase reference(PHR) signal at 704. In some embodiments, the method 700 comprisesselecting at least one of the first fractional phase signal or thesecond fractional phase signal based on a phase error (PHE) signal at706.

FIG. 8 is a flow diagram of an example method 800 for locking a phaselocked loop (PLL), according to some embodiments. In some embodiments, afrequency command word (FCW) is set and a phase locked loop (PLL) isturned on at 802. In some embodiments, frequency settling occurs at 804.In some embodiments, frequency settling is repeated via 806A until aphase error (PHE) is less than a DCO period. Continuing at 806B to 808,phase settling is enabled when a multi-phase TDC is enabled. At 810, thefirst phase finder it turned on, and operates continuously 812A untilthe PHE is less than at least about ninety degrees at 812. When the PHEis less than ninety degrees, the method continues at 812B. At 814, thefirst phase finder is turned off, and the second phase finder is turnedon at 816. In some embodiments, the second phase finder operates until athreshold is met at 818. At 820, the PLL is locked.

FIG. 9 is a flow diagram of an example method 900 for designing a phaselocked loop (PLL), according to some embodiments. In some embodiments, aDCO period is determined at 902. In some embodiments, a TDC resolutionis determined at 904. For example, an inverter delay time is selected at904. In some embodiments, a number of DCO phases associated with amulti-phase CKV is determined at 906. For example, a multi-phase CKV isfour phases, eight phases, etc. In some embodiments, TDC is set at 908.In some embodiments, at least one of a phase predictor, first phasefinder, second phase finder, or a phase switch is designed based on thenumber of phases at 910, 912, 914, and 916.

According to some aspects, a multi-phase time-to-digital converter (TDC)for a phase locked loop (PLL) is provided, comprising a first phasefinder, a phase predictor, a second phase finder, and a phase switch. Insome embodiments, the first phase finder is configured to generate afirst fractional phase signal of a multi-phase variable clock (CKV)signal based on at least one of the multi-phase CKV signal or areference frequency (FREF) signal. In some embodiments, the multi-phaseCKV signal is associated with one or more clock signals and one or morecorresponding phases. In some embodiments, phase predictor is configuredto generate a phase select (QSEL) signal associated with a fractionalfrequency command word (FCW) signal based on at least one of a FCWsignal or a phase reference (PHR) signal. In some embodiments, phasepredictor is configured to generate a multi-phase CKV select (CKVSEL)signal corresponding to a clock signal of the one or more clock signalsand a phase of the one or more corresponding phases based on at leastone of the multi-phase CKV signal or the QSEL signal. In someembodiments, the second phase finder is configured to generate a secondfractional phase signal of the multi-phase CKV signal based on at leastone of the CKVSEL signal or the QSEL signal. In some embodiments, thephase switch is configured to select at least one of the firstfractional phase signal or the second fractional phase signal based on aphase error (PHE) signal.

According to some aspects, a phase locked loop (PLL) is provided,comprising an accumulator component. In some embodiments, the PLLcomprises an adder component connected to the accumulator component. Insome embodiments, the PLL comprises a loop filter connected to the addercomponent. In some embodiments, the PLL comprises a digitally controlledoscillator (DCO) connected to the loop filter. In some embodiments, thePLL comprises a sigma delta modulation component connected to at leastone of the DCO or the loop filter. In some embodiments, the PLLcomprises a counter component connected to at least one of the DCO orthe adder component. In some embodiments, the PLL comprises amulti-phase time-to-digital converter (TDC). In some embodiments, themulti-phase TDC comprises a first phase finder connected to the DCO. Insome embodiments, the multi-phase TDC comprises a phase predictorconnected to the DCO. In some embodiments, the multi-phase TDC comprisesa second phase finder connected to the phase predictor. In someembodiments, the multi-phase TDC comprises a phase switch connected toat least one of the first phase finder, the second phase finder, or theadder component.

According to some aspects, a method for locking a phase locked loop(PLL) is provided, comprising generating a first fractional phase signalof a multi-phase variable clock (CKV) signal based on at least one ofthe multi-phase CKV signal or a reference frequency (FREF) signal, themulti-phase CKV signal associated with one or more clock signals and oneor more corresponding phases. In some embodiments, the method comprisesgenerating a second fractional phase signal of the multi-phase CKVsignal based on at least one of the multi-phase CKV signal, a frequencycommand word (FCW) signal, or a phase reference (PHR) signal. In someembodiments, the method comprises selecting at least one of the firstfractional phase signal or the second fractional phase signal based on aphase error (PHE) signal.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter of the appended claims is not necessarily limited tothe specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as example forms ofimplementing the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued as to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated based on thisdescription. Further, it will be understood that not all operations arenecessarily present in each embodiment provided herein.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB or both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used in either the detaileddescription or the claims, such terms are intended to be inclusive in amanner similar to the term “comprising”.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur based on a reading and understanding of this specificationand the annexed drawings. The disclosure includes all such modificationsand alterations and is limited only by the scope of the followingclaims.

What is claimed is:
 1. A multi-phase time-to-digital converter (TDC) fora phase locked loop (PLL), comprising: a phase predictor configured togenerate a multi-phase variable clock select (CKVSEL) signal based on atleast one of a multi-phase variable clock (CKV) signal or a phase select(QSEL) signal; a phase finder configured to generate a fractional phasesignal of the multi-phase CKV signal based on at least one of the CKVSELsignal or the QSEL signal; and a phase switch configured to generate afractional variable phase correction (PHVF) signal based on thefractional phase signal when a phase error (PHE) signal applied to thephase switch is greater than a first threshold.
 2. The multi-phase TDCof claim 1, comprising: a second phase finder configured to generate asecond fractional phase signal of the multi-phase CKV signal based on atleast one of the multi-phase CKV signal or a reference frequency (FREF)signal.
 3. The multi-phase TDC of claim 2, the phase switch configuredto generate the PHVF signal based on the second fractional phase signalwhen the PHE signal is less than or equal to the first threshold.
 4. Themulti-phase TDC of claim 1, the first threshold a function of a numberof phases associated with the multi-phase CKV signal.
 5. The multi-phaseTDC of claim 1, the phase predictor configured to generate the QSELsignal based on at least one of a frequency command word (FCW) signal ora phase reference (PHR) signal.
 6. The multi-phase TDC of claim 1, themulti-phase CKV signal associated with a first clock signal having afirst phase and a second clock signal having a second phase.
 7. Themulti-phase TDC of claim 6, the phase predictor configured to select,from the multi-phase CKV signal, the first clock signal to generate themulti-phase CKVSEL signal.
 8. The multi-phase TDC of claim 1, themulti-phase CKV signal corresponding to a 4-phase CKV signal.
 9. Themulti-phase TDC of claim 1, the first threshold corresponding to 90degrees.
 10. A phase locked loop (PLL), comprising: a multi-phasetime-to-digital converter (TDC), comprising: a first phase finderconnected to a digitally controlled oscillator (DCO); a phase predictorconnected to the DCO; a second phase finder connected to the phasepredictor; and a phase switch connected to at least one of the firstphase finder or the second phase finder.
 11. The PLL of claim 10, thephase switch connected to the first phase finder and the second phasefinder.
 12. The PLL of claim 10, the phase switch configured to:generate a fractional variable phase correction (PHVF) signal based on afirst fractional phase signal generated by the first phase finder when aphase error (PHE) signal is less than or equal to a first threshold, andgenerate the PHVF signal based on a second fractional phase signalgenerated by the second phase finder when the PHE signal is greater thanthe first threshold.
 13. The PLL of claim 10, the DCO configured togenerate a multi-phase variable clock (CKV) signal associated with afirst clock signal having a first phase and a second clock signal havinga second phase.
 14. The PLL of claim 10, the phase switch configured todisable the second phase finder when the first phase finder is enabled.15. The PLL of claim 10, the phase switch configured to enable thesecond phase finder when the first phase finder is disabled.
 16. Amethod for locking a phase locked loop (PLL), comprising: generating afirst fractional phase signal of a multi-phase variable clock (CKV)signal based on the multi-phase CKV signal and a reference frequency(FREF) signal, the multi-phase CKV signal associated with a first clocksignal having a first phase and a second clock signal having a secondphase.
 17. The method of claim 16, comprising: generating a secondfractional phase signal of the multi-phase CKV signal based on a phaseselect (QSEL) signal.
 18. The method of claim 17, comprising: generatinga fractional variable phase correction (PHVF) signal based on at leastone of the first fractional phase signal or the second fractional phasesignal.
 19. The method of claim 17, comprising: generating the QSELsignal based upon a phase reference (PHR) signal and a frequency commandword (FCW) signal.
 20. The method of claim 17, comprising: generating afractional variable phase correction (PHVF) signal based on the firstfractional phase signal when a phase error (PHE) signal is less than orequal to a first threshold; and generating the PHVF signal based on thesecond fractional phase signal when the PHE signal is greater than thefirst threshold.